24iG Geology of 



repose on the decomposed surface of the melaphyres or on the palseozoic 

 rocks, generally appearing below the former, altered and impregnated 

 with siliceous matter. In the tufas at their base we find impressions of 

 leaves, but too indistinct for description, and trunks of monocotyledonous 

 trees, often of enormous size, of which the bark has been silicified, 

 showing its original structure, whilst the hollow interior appears as a 

 dense mass of semi-opal or flint. 



In Banks' Peninsula, where we meet with a partly altered nucleus 

 of palaeozoic rocks (schists), a small zone of quartziferous porphyry 

 and tufa appears near it, which may be of the same age as the belt of 

 acidic eruptive rocks west and south-west of it. Whilst the highest 

 points of the older basic eruptions rise in the Clent Hills to 4212 feet, 

 the acidic rocks reach a still higher level in Mount Somers, namely, 

 5240 feet, both being situated due west of Banks' Peninsula, and due 

 east of Mount Cook. 



It is a remarkable fact that here, where the Southern Alps attain 

 their highest elevation, the mountains are not only much narrowed in 

 lateral extent, but the island itself is also much compressed, notwith- 

 standing the great extension of the eruptive rocks, if we do not take 

 the Canterbury plains into consideration. It thus appears that the 

 abyssological forces, by forming here the highest foldings, did so at 

 the expense of the breadth ; moreover, it is clear that the highest 

 mountains, being the greatest condensers of humidity, could offer an 

 enormous supply from their neves to the gigantic glaciers at their 

 base, and thus aid effectually in their own destruction. 



A similar zone of basic eruptive rocks exists along the West 

 Coast nearly opposite to that on the eastern side, but it would 

 be difficult to settle their contemporaneous origin from lithological 

 character alone, no fossils having hitherto been found in the 

 tufas belonging to them and lying at their base. On the eastern 

 side of the Southern Alps, the acidic rocks have furnished the 

 material for extensive beds of tufas, and conglomerates reposing 

 upon them, and from the palaeozoic rocks similar beds have been 

 derived in their neighbourhood. They form the lowest portion of an 

 important series of beds which are of a highly economic value, not 

 only in Canterbury but all over Xew Zealand. It is evident that the 

 land was gradually rising, so that the porphyries came within the 

 influence of the tides and currents of the sea, by which they were 

 partly destroyed, and that afterwards a shallow sandy shore fringed 



